To communicate with the network, mobile phones radiate electromagnetic waves when being used. The antennas in these wireless devices are used for receiving and radiating transmitted signal for communication. Signal quality parameters are not the only one to taken into account in designing the antenna system of mobile device but it is also important to make sure that the user RF exposure levels Specific Absorption Rate (SAR) are within compliance and standards. Mobile devices are handled close against different environments and platforms, depends upon usage scenarios that causes electromagnetic interaction with environments based on its properties which in turn can leads to degradation of signal quality. Also device orientation change according to usage can leads to power loss due to polarization mismatch. In scenarios like when the signal quality is weak the fixed radiation pattern design without sensing the nature of environment and orientation can leads to radiations in directions that are less effective which in turn causes degradation in signal quality and loss of valuable battery power. In case of Multiple-Input Multiple-Output (MIMO) antenna arrays, the performance is very sensitive to the implementation of the antennas, the environment in which the devices is being used and even the orientation of the device itself. This means that a small change in the position of the device in use can result in significant change in data rate. For example, the user experience of a downloading speed or streaming video etcetera could go from excellent to marginal or poor just because the device was moved slightly during usage. Moreover, the presence of user hand and body cause radiation pattern distortion or detuning of the antennas and absorption of the radiation, thus affecting the efficiency and correlation performance of the antenna array. The constant mobility of the mobile device when in usage further reinforces the need for sustainable performance.
It is not been proved that the generally handled positions of mobile phones to be absolutely safe and is not hazardous. World Health Organization (WHO) has classified mobile phone radiation as possibly carcinogenic. The WHO has also concluded that the precautionary approach is an appropriate response to the lack of scientific consensus regarding the long term health effects of exposure to cell phone radiation. An IEEE journal on Microwave Theory and Techniques shows that the penetration level of radiation is more in children's as the width of skull is less and can also have effect on baby of pregnant women's. The Journal of the American Medical Association by researchers from the National Institute of Health and the Brookhaven National Lab identifies effect showing through their experiments that holding a cell phone to the ear increases the metabolic activity of nearby brain tissue. In addition to cancer issue lot of other possible health concerns the radiation can leads to are electromagnetic hypersensitivity, thermal or heating effect, non-thermal effect, genotoxic effect, fatigue, loss of memory, cognitive effect, sleep effect, ringing ears, effect on electro-medical devices like pacemaker and hearing aid etcetera. Several studies investigating the potential health effects of radiation on brain electrical activity, joint pain, heart rate, blood pressure, immune system are under the way. Research conducted regarding health concerns of radiation have increased, papers are published and researches are carried on regarding the long term effects of radiation and its medical complications. Generally these researches will take long time to produce results advanced clinical report and by that time the effect caused by the radiation can be substantial like for example smoking causes lung cancer, tobacco usage causes mouth cancer etcetera are confirmed after many years of study. The mobile phones have become an essential part of many lives not only for communication but also to handle safety and emergency situations. Regulatory Government bodies around the world have adopted international safety guidelines developed by scientific organizations governing the exposure to RF radiation and the mobile phones are designed to operate within these stringent limits. Specific Absorption Rate (SAR) is the measure of amount of radiation or electromagnetic energy absorbed by the body when exposed to radiating devices like mobile phone and has unit of watts per kilogram W/kg. It's difficult to build an antenna system with more filed strength for better communication and reduced SAR to protect the user from radiation. Most of the radiation shielding products like stickers covers etcetera available in the market works in standalone mode which is not smart enough or closed loop design to work efficiently according to various scenarios. Some can also hamper the radiated power that leads to negative impact by reducing the signal quality which in turn makes the antenna system to increase the transmitting power level to maintain communication thereby reducing the battery life.
Sensing the change in mobile device environment with its property plays an important role due to electromagnetic interaction with these environments. But currently the antenna system or radiation protection designs are not much concerned about detecting the change in nature or property of device environment and device orientation to control the radiation pattern which is essential in optimizing signal quality as well as protecting the user form radiation. There are some designs to reduce SAR and the main drawback with these designs that uses power regulator, power governing systems etcetera are it mainly focus on reducing the overall transmit power levels which in turn reduces the signal strength and the possibility of the signal to reach the base station that affects the quality of communication. Environment, orientation, location, position etcetera of a mobile device are not a constant in real world scenarios and mostly the antenna system tested in lab are just designed to perform optimally in some scenarios which won't help to efficiently enhance the performance. It is hard for an antenna system just with existing signal quality parameters to act smartly according to scenarios without actively sensing the above mentioned parameters. As the mobile device environment and orientation changes the fixed radiation pattern can also leads to power loss due to radiation in less effective directions.